Catalytic zeolite membrane reactors for the selective CO oxidation
Clean H2
Paola Bernardo, Catia Algieri, Giuseppe Barbieri, Enrico Drioli
Istituto per la Tecnologia delle Membrane (ITM-CNR), Rende CS, Italy
Pt
www.itm.cnr.it
CO
CO selective oxidation (Selox)
2 CO + O2 → 2 CO2
This work
Interesting and economic approach for CO removal from
H2–rich gas streams (less than 50 ppm for PEMFCs applications).
• Na-Y zeolite membranes prepared by Secondary growth
Zeolites
Regular structure (micropores of molecular size)
Thermal and chemical stability (up to 600-700°C)
Continuous Seeding (tubular supports)
Properties can be adjusted (varying the Si/Al ratio
Pt–supported catalysts
or by cation-exchange)
Seeding A: no DP
Seeding B: Cross-flow filtration, DP>0
Key-factor : pH
Membrane preparation
Seeding
Support
Zeolite crystal
suspension
+
Seeded Support
Sodium silicate
solution
Sodium
hydroxide
+
Supported Zeolite Membrane
Zeolite film
+
Mixing
+
• Pt-loaded Zeolitic Catalytic Membranes for CO Selox
Compromise between costs and good functionality.
Catalytic activity
Sodium
aluminate
H2
Deionized
+
water
Electrostatic interaction
Synthesis solution
a-Al2O3 pzc = 9 + + + + + + + + + - - - - - - - -
Growth (90°C)
a-Al2O3 support
Washing and
drying
Na-X pzc = 10
By Ion-exchange
Calcination and Reduction
Catalytic Zeolite
membrane
+ + + +++++++++++++--
Zeolite membrane
pH
9
10
Permeation tests (room temperature, DP up to 1 bar)
Seeding A, no DP
Seeding B, DP>0
MRs with a catalytic membrane
80
H2
N2
H2
Permeance, micromol/m s Pa
H2 support (dpore = 60 nm)
60
40
2
2
Permeance, micromol/m s Pa
80
H2
N2 support (dpore = 60 nm)
20
N2
H2 - support (dpore = 100 nm)
• Selective permeation + Pt catalytic activity
60
20
40
60
C atalytic
m em brane
• Reduced by-pass with respect to fixed bed
40
N2 - support (dpore = 100 nm)
H2
20
0
0
Flow – through MR
• Zeolitic layer (few microns thick), low pressure drops
N2
N2
80
0
0
Seeding velocity, cm/min
20
40
60
80
100
Seeding stage  cut 
2
=  XCO , %
l
Seeding stage-cut, %
F Permeate
F Feed
Selox MR Reaction tests (T = 200°C, Feed = ca. 600 cc (STP)/min)
YCO 2 
Permeate
CO
Feed
CO
Formed
FCO2
Feed
FO2
The Pt–Y catalytic MRs expand the CO
conversion-selectivity region, even with
lower space-time values [ca. 1 mgPt
min/cm3(STP)] than Pt–based TRs (at
200°C),
as
reported
in
the
literature [1].
200
2.0
○ O2:CO:H2
∗ O2:CO:H2:N2
□ O2:CO:H2:N2
△O2:CO:H2:N2
● O2:CO:H2 N2:CO2
150
1.5
= 1 : 1 : 98
= 1: 1 : 87 :11
= 1 : 1 : 61 : 37
= 1 : 0.9 : 59.5 :38.6
= 1 : 0.9 : 60.2 : 22.7 : 15.2
open
2 bar
100
1.0
[b]
[b]
[b]
[c]
[c]
150
3 bar
100
2.6 bar
l =
2.2
2 bar
50
0.5
2b,
11%
N2 N2
= 11%
2b,
CO2,
23%
N2 w
= ith
23%
CON2
2= 15%
2b,
CO2, N2 37%
N2 no
= 37%
H,
N2N2
= 37% m=0.94
N2N2
= 37% m=1.01
H,
N2N2
= 48% M=1.01
H,
4 bar
CO out, ppm
F
F
Feed
CO
F
Pt-Y membranes (b and c) prepared by Seeding A
Feed
,-
X CO 
O2
CO
CO2 = 2 XO2 S
Y CO 2 =Y2
X O2 S , %
l 2
Seeding A
50
l=2
Seeding B
0
0
0
0
20
0.2
[c]
[c]
[c]
[d]
[d]
[d]
40
0.4
60
0.6
80
0.8
100
1.0
-
CO conversion , %
0
1
2
3 , bar
PFeed
4
5
P , bar
CONCLUSIONS
 Tubular zeolite (FAU) membranes were prepared by a continuous seeding.
 The cross-flow filtration seeding (Seeding B) resulted in an improved membrane quality.
 Pt-loaded (by ion-exchange) membranes were used in MRs for the H2 purification by means of CO Selox.
 Membranes prepared by Seeding A: Improved MR performance by increasing the operating pressure and the N2% in the feed (realistic stream; H2 ca. 60%).
 The improved membrane quality (Seeding B) resulted in reduced CO amount operating at the same conditions as the membranes prepared by Seeding A.
References: [1] P. Bernardo, C. Algieri, G. Barbieri, E. Drioli, Catalytic (Pt–Y) membranes for the purification of H2–rich streams, Catalysis Today (2006), in press.
Acknowledgments: Progetto di ricerca “CAMERE RBNE03JCR5 – Nuove membrane catalitiche e reattori catalitici a membrana per reazioni selettive come sistemi avanzati per uno sviluppo sostenibile” funded by the Italian Ministry of
Education, University and Research (MIUR).